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Severe Weather Event 2-3 February 2005

Contents of page: Weather Pattern | Rainfall | Snow | Temperature | Wind | Dust

An unusually intense low-pressure system developed over Eastern Bass Strait on 2^nd February 2005. After a spell of warm days with a north to north easterly airflow over much of eastern Australia, the region suffered the effects of one of the most intense summer time weather systems on record. Southern NSW, South Australia and Tasmania also received substantial rainfall during this event, however the highest rainfalls were concentrated in Victoria. The event made February 2005, Victoria's wettest February since 1973 and the 7^th wettest in the last 106 years. The cold air associated with this system also assisted in the month of February in Victoria being its coolest since 1954. Many rainfall and temperature records were broken in the course of the event as the system passed across eastern Australia.

Figure 1. Satellite image of the storm over Victoria at at 0225 UTC (1325 EDST) on 3rd February. Satellite image originally processed by the Bureau of Meteorology from the geostationary satellite GOES-9 operated by the National Oceanographic and Atmospheric Administration for the Japan Meteorological Agency.

The system brought abnormally low temperatures and severe storms with gale and storm force winds to most parts of the region. However, the continuous rainfall for about 30 hours was perhaps the most significant feature produced by the low-pressure system. The rainfall resulted in widespread flooding, particularly over Central Victoria and West and South Gippsland. Unseasonal snowfalls were observed on the Australian Alps. Although low-pressure systems in February are not uncommon, the slow and westward moving nature of this particular system was extraordinary. The centre of the low developed and deepened over Melbourne with very little movement. The combination of extreme rainfall and lashing winds left a trail of destruction.

Weather Pattern

Figure 2. Mean Sea Level Pressure analysis for 0000UTC (11am EDST) on 3rd February.

The synoptic weather pattern for the 1^st February indicated a significant cold front with a substantial cold air mass crossing the Southern Ocean towards southeastern Australia. The cold air is depicted on the satellite imagery as an extensive area of speckled cumulus cloud.

On 2^nd February, the deep layer of cold air, in conjunction with a strong upper jet, resulted in a significant surface cyclone developing along the front as it passed over New South Wales and Victoria. The low-pressure system 'bombed' between the boundary of extremely cold air from the southern ocean and the warm, moist air originating from the Tasman Sea. The rapid development of a low or intensification of a pre-existing one is known meteorologically as cyclogenesis.

The upper level flow displayed classical characteristics supporting cyclogenesis over Victoria. Several of these features include the amplification of an upper trough and strength of the northerly jet on the eastward flank of the trough. Observations suggest that wind speeds associated with the jet were in excess of 200 km/h over Victoria. The presence of a strong upper level jet is evident in the satellite imagery by marked cloud banding perpendicular to the upper flow and also with the presence of dry air adjacent to the cloud band. A dry 'slot' often assists with the intensification of an upper trough.

The low originally developed over southern New South Wales before moving toward Gabo Island on 2^nd February. The low then tracked westwards toward Central Victoria and deepened rapidly to below 985hPa in the early hours of 3^rd February. The low then remained quasi-stationary over Central Victoria on the 3^rd February before gradually weakening as it moved eastwards on the morning of the 4^th February.

Rainfall

Extreme rainfall totals were recorded over large areas of Gippsland and central Victoria, with 24-hour rainfall totals to 9am on the 3^rd February in excess of 150mm at some places. The rain began falling during the evening of the 1^st February; it then rained all day on Wednesday the 2^nd before intensifying overnight as the system intensified. Rain did not cease until the Thursday morning over Central Victoria, having rained continuously for over 30 hours.

Figure 3. Rainfall totals for the event across Victoria.

In Melbourne there was a combined total rainfall of 138mm for the event, of which 113mm was received in the 24-hour period to 9am on 3^rd February, just eclipsing the previous record of 108mm on 29^th January 1963. To put this rainfall event in perspective, the 138mm of rain recorded in the city gauge represents 21% of the average yearly rainfall of 653mm. In fact, records indicate that this was also the highest two-day rainfall total ever recorded in the city's rain gauge. For a full list of rainfall records from this event, click the Rainfall Records link at the top of this page.

Figure 4. Graph of cumulative rainfall at Melbourne City during the event.

The prolonged nature of this rainfall event combined with periods of intense rainfall resulted in significant riverine flooding. The Yarra River at Collingwood broke its banks for the first time since 1934. In Melbourne, major flooding was also experienced along the Dandenong and Kororoit Creeks. The Tanjil River at Tanjil Junction and Sunday Creek at Tallarook also experienced major flooding. Other Victorian rivers and creeks in the state's northeast had minor or moderate flooding.

Figure 5. Flooding at Rockbank in Melbourne on 3rd February (picture courtesy of Shawn Smits).

Snow

The Alpine region received unseasonal snowfall. According to staff at Mt Hotham and Falls Creek Resorts there was up to 20cm of snow covering the ground as the cold air surged over Victoria in the wake of the low. Whilst it is not unusual for Alpine locations to experience one or two days of very light and brief snowfalls during the warmer months of the year, this particular event was unusual due to the exceptionally low temperatures and amount of snowfall.

Temperature

Many locations witnessed their coldest February day on record, with maximum temperatures struggling to get into the 'teens'. Several locations around Melbourne recorded their lowest maximum temperature for a February day, including Melbourne Airport with a maximum of 13.5°C. Ballarat only managed a maximum of 10°C. For a full list of temperature records from this event, click the Temperature Records link at the top of this page.

Wind

The rapid deepening of the low-pressure system resulted in widespread gale force winds across most parts of the southern and central Victoria, with exposed coastal locations reaching storm force at times. Gusts of up to 148km/hr were recorded at Wilsons Promontory Lighthouse, while Fawkner Beacon, located on Port Phillip Bay, recorded the strongest gust in the Melbourne area with 104km/hr during the early hours of Thursday morning. The wind force was such that coastal waters, such as Point Nepean, recorded a peak wave height of 12.5 metres.

Dust

In other parts of Australia the low and associated front produced extensive dust storms in New South Wales, South Australia and western parts of Queensland. Suspended dust from the vicinity of Lake Eyre actually reached the Kimberly region on the 3^rd of February, travelling in the southeast flow over northern Western Australia. A major dust storm was reported in Brisbane, while dust storm in western NSW brought the visibility to a mere 500 metres at Bourke.